Electrosurgical procedures typically rely on the application of high frequency, for example radiofrequency (RF), energy to treat, cut, ablate or coagulate tissue structures such as, for example, neural tissue. The high frequency energy is often delivered to a region of tissue from an energy source such as a generator via an active electrode of a probe that is inserted into a patient's body. The resistance of tissue, located proximate the active electrode of the probe, to the high frequency energy, causes the tissue temperature to rise. If the temperature is increased past a certain tissue-dependent level, referred to as the lesioning temperature, tissue damage will occur, and a lesion will form. Often, the tissue proximate to the probe heats up faster than tissue farther away from the probe, which may limit the size of the lesion.
In addition to limited lesion size, prior art devices typically form lesions with minimal extension distal to the tip of the electrode, as described by Bogduk et al. (Neurosurgery, 20(4):529-535, 1987) and as shown in FIG. 16 (FIG. 4 of the Bogduk article). Prior art devices typically include an electrically exposed conductive portion along the length of the device. Bogduk et al. suggest that failures of such prior art devices to effectively lesion target tissue was due to the fact that lesions created by those devices do not extend distal to the distal tip of the devices but rather extend primarily circumferentially to the distal tip, along the length of the exposed conductive portions. Bogduk et al. proceed to suggest that probe electrodes should be positioned such that they run parallel to the target nerve for optimal efficacy.
Scientific literature published since Bogduk et al's study continue to emphasize the importance of positioning the electrodes parallel to, as opposed to perpendicular to, the target site, since the general structure of probe electrodes, specifically the exposed conductive portion, has not changed significantly since Bogduk et al's study. For example, Lord et al. (Neurosurgery 36(4):732-739, 1995) note that the electrodes must lie parallel to the nerve for the nerve to be incorporated in the radial lesion. In addition, Hooten et al. (Pain Medicine, 6(2):129-138, 2005) also conclude that, due to the characteristics of prior art probes and lesions formed therefrom, the probes should be placed parallel to the course of the target nerve in order to be effective.
A parallel approach may be difficult and time consuming for a user and it would therefore be advantageous to have a device capable of creating a lesion extending further distal to the probe, as well as a method describing a more perpendicular approach than has previously been possible. Thus, methods and devices that overcome some or all of the deficiencies associated with the prior art are desired.